Rails 2.1 introduced some nifty ways to manage gems that your Rails
application depends upon. However, using gems *instead of* plugins
seems to a growing practice as well.
I'm just wondering why this is? Installing a plugin means
- plugins are downloaded from a remote source and copied into vendor/
plugins
- Rails automatically finds code in vendor/plugins
rake gems:install in Rails 2.1 means:
- gems can downloaded from a remote source and "unpacked" (source
copied) into vendor/gems
- Rails automatically finds code in vendor/gems
What is the rationale for preferring one over the other?
The main advantage I see of gems is finer-grained control over the
version of the gem you will allow your app to use (a non-issue if you
unpack anyway).
I have wondered this very same thing so hopefully someone can provide
some insight into it.
I do however believe that a gem is available system-wide, where a
plugin is only available to the particular application that it is
installed in. Is that correct anyone?
That is correct, but is a double-edged sword. For the same reason it's
best to "freeze" rails to your app so that you're not dependent on the
system-wide Rails gems (unexpected upgrades or downgrades), I think
most people will also "freeze" (unpack) their gems into their app as
well.
Perhaps the main advantage is to simply have the choice. I can install
gems once without replication if many apps use the same gems (like
will_paginate, pdf-writer, etc.) if I'm willing to rely on system-wide
gems. Or, I can choose to unpack if I wish.
Whereas with plugins, you could easily do the same by symlinking
vendor/plugins to a shared directory on your server, but perhaps this
wasn't obvious to many people.
There is one advantage that I see with gems over plugins: If I'm away
from an internet connection working on my application and get to a point
that I need to use a gem/plugin it's easier with a gem. I can simply
vendor it (or just use it). But, unless I have previously downloaded and
stored a plugin somewhere on my local hard drive, I'm stuck.
Not that it's is much different than with a gem I might not have, but
I'm saying the likelihood of having a commonly used gem installed is
higher than the case for a plugin.
